e36M42 1994 engine losing power from 2500rpm onward!

[selespeed]

this is puzzling...

i have the e36m42 april 1994 engine swapped into my e30 manual. the engine fired up. but subsequent starting up does not fire up at first crank.

but here's the annoying part - the engine is LOSING POWER from 2500rpm onward. when accelerating hard, it tends to give a "diving" feeling as if there is some kind of vaccum. also, the engine exhibits noticebly ROUGH when revving from 2500 rpm onward. the steering wheel is shaking - tested when car is stationery. from rest to 2500rpm it appears normal!

i have the new NGK spark plugs installed though.

i have swapped the AFM with another good one and it is still showing similar symptoms. i can't see anything from diagnostics. once i stopped the engine, it takes more than one crank to restart engine.

all those experts out there, please help.

[Slowered318]

I had a similar problem after rebuilding my engine. It ended up being the crank position sensor (PN 12141247259) was damaged.

[selespeed]

thank you for the reply.

i am actually curious how crank sensor can cause this power loss... care to explain how?

my friend tested today and there're signs of misfirings too. i will get a crank sensor to try it. thank you once again.

selespeed

[DesktopDave]

No need to replace it until you've tested it.  You'll need to see about 680 ohms between terminals 1 & 2 of the sensor.  Terminal pairs 1 & 3 and 2 & 3 should have very high resistance, like over 10K ohms.  Readings should also be very steady, and the sensor head should be clean of metal filings.

If that crank sensor isn't getting readings, it'll cut power to the fuel pump relay.  So if you're getting a few misses on the crank sensor, you may get some rough running.  Oddly, even if this is happening, the DME will not set a code.

[Slowered318]

thank you for the reply.

i am actually curious how crank sensor can cause this power loss... care to explain how?

my friend tested today and there're signs of misfirings too. i will get a crank sensor to try it. thank you once again.

selespeed

You should test the sensor first like DesktopDave recommended, it's too expensive to just swap out on a hunch.

I'm not exactly sure why but I couldn't run above 3000 rpm. My mechanic and I went over the whole engine and noticed one side of the sensor was dented in.

[selespeed]

thank you all for the suggestions and advice. i will do this on monday and report the findings.

[selespeed]

i bought a new crank sensor and replaced it. at the same time i also replaced the coil with another good one. there's no misfiring. the engine is noticably stronger from start-off upto around 3000 rpm or so. but it still exhibits the same rounghness or vibration at around 2400rpm to 4000 rpm. and i still can't pull properly under hard acceleration. floor it, it just can't go, as if something got stuck!

what's can be wrong?

1. plug cables?
2. vaccum leaks somewhere?
3. DISA valve malfunction?
4. fuel pressure?
5. some sensors not plugged in?

please help!

[ti_tony]

Per this forum... fuel pressure.

[selespeed]

i suspect it's fuel pressure...

but here's something interesting. while tesing the car today pulling at around 5000rpm trying to maintain this rpm on 4th gear, the engine suddenly developed drop in rpm like coughing - like a drop in plane air altitude for a few seconds. sounds like sputtering or misfiring? i have checked that vaccum hoses are properly plugged in. again, the usual symptoms of power loss from 2500+ remains!

could this be also sparks? lately, engine is also becoming rougher at lower rpm.